Derek Burnett
Derek Burnett is a Contributing Writer at Bottom Line Personal, where he writes frequently on health and wellness. He is also a contributing editor with Reader’s Digest magazine.
With so much of the world hyper-focused on trying to lose weight, it can be both alarming and isolating to find that you’re losing weight when you don’t want to. Perhaps you don’t like the way your sudden weight loss makes you look, or you may be concerned that it signals some kind of health problem. And indeed, there are many possible explanations for sudden unexplained weight loss, some of them more serious than others. Don’t ignore the situation just because friends or family might make dismissive comments like, “Gee, I wish I had that problem!”
Most doctors consider unintentional weight loss to be any significant drop in body mass not resulting from changes in diet and exercise. In other words, if your lifestyle hasn’t changed but you’ve suddenly begun dropping significant pounds, you’re experiencing unintentional weight loss and should investigate why.
But what is “significant” weight loss? After all, everyone’s weight fluctuates from time to time. If you’re under age 65, you should talk to a doctor if you’ve unintentionally lost 10 pounds, or 5% of your body weight, over a period of between six months and a year. For older adults, weight loss is considered “problematic” if the patient loses 5% of body weight in one month or 10% in six months.
Stress and anxiety. There appear to be two explanations for a link between anxiety and weight loss. The first is behavioral. If you’re too stressed out, you might have no appetite, and you could even forget to eat because you’re so focused on what’s bothering you. Often people whose weight loss is driven by stress aren’t even aware that their eating habits have changed. Ultra-stressed individuals may also be more physically active than they consciously realize, burning calories through pacing, fidgeting, and the inability to sit and relax.
But there’s also a probable physiological mechanism at play. In 2019, Scripps researchers discovered that both anxiety and weight loss are associated with the absence of a substance called brain-derived neurotropic factor (BDNF) in the brain region known as the amygdala. Even when fed a diet that should have made them obese, the researchers found, mice deprived of BDNF in the amygdala lost weight and displayed symptoms of anxiety.
Medications. Several different types of medications have been found to cause unintentional weight loss in some patients. Antihistamines, iron, potassium, decongestants, and antibiotics all may have this effect, as might the following list, which is not exhaustive:
Substance abuse. Unintentional weight loss could be a sign that your use of drugs or alcohol has become problematic. Such substances could affect your digestion, appetite, or metabolism.
Chronic infection. Living with tuberculosis or HIV can cause your metabolism to increase, requiring more calories to meet your daily needs and maintain your regular body weight.
Parasites. Gastrointestinal worms are no longer as common in the US as they once were, but several types do remain prevalent here. And if you travel internationally, you could become infected. Interestingly, the weight loss from worms is not because they steal all your nutrition. Instead, the body’s immune response to the presence of the parasites happens to release substances that diminish leptin, the hormone that tells you you’re hungry.
Overactive thyroid. When the thyroid gland produces too much thyroid hormone (a condition called hyperthyroidism), the body’s metabolism is significantly increased, making it harder to maintain body weight. Other symptoms of hyperthyroidism include hand tremors and irregular heartbeat.
Undiagnosed diabetes. Because so many people associate diabetes with obesity, they don’t consider that sudden effortless weight loss could possibly indicate that they have the disease. But it’s a common symptom of undiagnosed diabetes. In a person with untreated diabetes, cells can’t get energy from glucose in their food and instead turn to the body’s stores of fat and muscle. Accompanying symptoms often include excessive hunger and thirst.
Pancreatitis. The pancreas is an organ that produces enzymes and hormones that aid in digestion. When those enzymes attack a part of the pancreas itself, it becomes inflamed and painful, a condition called pancreatitis. People with pancreatitis often lose weight despite not making any changes to their diets, because the organ has begun secreting insufficient amounts of its enzymes for the body to properly digest food and absorb nutrients.
Cancer. It’s not uncommon for people with cancer to lose significant weight. Some have a hard time eating enough because they have trouble swallowing, experience stomach pain, have frequent nausea or vomiting spells, develop bowel blockages, or simply don’t adequately absorb nutrients from their food. Certain cancers appear to release chemicals into the bloodstream that cause muscle and fat to dissipate. Some people with cancer experience a condition called cachexia, or wasting syndrome, marked by diminished appetite, fatigue, and weight loss. About 60% of people with lung cancer experience such symptoms, as do 80% of those whose cancer is located in the upper gastrointestinal tract, including the esophagus, stomach, small bowel, pancreas, and liver.
In a 2024 study of 157,000 patients, unintentional weight loss was associated with significantly increased risk of diagnosis of several cancers, including esophageal, pancreatic, stomach, biliary tract, liver, non-Hodgkin lymphoma, leukemia, multiple myeloma, colorectal, and lung. There was no association with breast cancer, brain cancer or melanoma.
Dental problems and mouth sores. Bad oral health can cause people to eat less. Poor-fitting dentures, lesions, cavities, tooth loss, inability to chew, inflammation, gum disease, temporomandibular joint syndrome (TMJ) and similar conditions can cause food aversions and avoidance. While it might seem that it would be obvious to someone that they weren’t eating as much because of pain in their mouths, the decrease in eating may be subtle but significant. And even when a person with dental problems eats just as much as ever, they may not chew their food as thoroughly, resulting in worse digestion and thus less absorption of nutrients.
What to do about your weight loss
How you and your doctor address your weight loss will depend upon what’s causing it. For example, if you’ve been unconsciously eating less because you have cavities in both sides of your mouth and eating has become unpleasant, the obvious solution would be to get your teeth fixed. If a medication is causing you to lose weight, you might be able to find an alternative drug that doesn’t have that side effect.
If you’ve developed a nutritional deficiency, your doctor may refer you to a dietician or put you on a supplement or special diet. But you won’t be able to fix the problem if you don’t face it head-on by opening a conversation with your doctor. If you visit a doctor regularly, they should weigh you each time you come in and proactively ask you about significant weight loss. But don’t count on that. If you have concerns about your body weight, raise them. Your doctor could simply be too distracted to notice.
